Set Appliance State:

Isolate Mains Power to appliance as per TOPs P4
Set Multimeter to Resistance Set meter to measure resistance
Disconnect connector X2 from the PCB

Measurement:

Test 1:
Measure the resistance between pin 3 (brown) and pin 4 (blue) of the disconnected X2 plug.
Resistance should be greater than 1M Ohm.
Test 2:
Measure the resistance between pin 3 (brown) on X2 to a suitable earth point.
Resistance should be greater than 1M Ohm.